1. Field of the Invention
This invention relates to a head shifting apparatus, and more particularly to a head shifting apparatus for shifting a head intermittently or stepwise relative to a recording medium.
2. Description of the Prior Art
Most of the recording or reproducing apparatus of the type using disc-shaped recording media, for example, magnetic sheets, employ a shifting mechanism for advancing the recording or reproducing head, track by track, in a radial direction of the recording medium, including a step motor and a shifting screw connected to the output shaft of the motor. For determining the basic shifting motion increment of the stepping motor in order to improve the precisional accuracy, the technique of shifting of the head by one step for the required advance (equal to each track pitch, for example) is inferior to that obtained by a plurality of steps. The technique of using a plurality of steps applies, for example, when the step motor is of the 4-phase type and four steps for the same track pitch is employed, as is well known in the art. Therefore, in the prior art apparatus, the use of multi-step shifting mechanisms prevails.
Another important aspect of this type of recording or reproducing apparatus is that whether in the recording or reproducing mode, means must be provided for detecting when the head is set at a predetermined reference position relative to the recording medium. As is the common practice in the art, it is through the same number of steps for each track pitch that the head is shifted in a direction to the limit position. The head is then shifted in the opposite direction, track to track. With such shifting control means, however, as will be fully described later, when the shifting steps of the head are disturbed by external disturbances, the head cannot be accurately aligned with the reference position. This leads to poor instrument compatibility.
Therefore, the general object of this invention is to eliminate all the above drawbacks of the prior art apparatus, and to provide a novel head shifting apparatus.
Another object of the invention is to provide a head shifting apparatus enabling the head to be automatically set at a predetermined reference position with remarkably increased accuracy, thereby making it possible to reduce the tracking error on the recording medium and to increase instrument compatibility.